Camera-based systems have been proposed, such as in commonly assigned patent application Ser. No. 09/372,915, filed Aug. 12, 1999, now U.S. Pat. No. 6,396,397, the disclosure of which is hereby incorporated herein by reference, that detect and display the presence, position of, distance to and rate of approach of vehicles, motorcycles, bicyclists, and the like, approaching a vehicle such as approaching from behind to overtake in a side lane to the vehicle. The image captured by such vehicular image capture systems can be displayed as a real-time image or by icons on a video screen, and with distances, rates of approach and object identifiers being displayed by indicia and/or overlays, such as is disclosed in U.S. Pat. Nos. 5,670,935; 5,949,331 and 6,222,447, the disclosures of which are hereby incorporated herein by reference. Such prior art systems work well. However, it is desirable for a vehicle driver to have visual access to the full 360 degrees surrounding the vehicle. It is not uncommon, however, for a vehicle driver to experience blind spots due to the design of the vehicle bodywork, windows and the rearview mirror system. A blind spot commonly exists between the field of view available to the driver through the exterior rearview mirror and the driver's peripheral limit of sight. Blind Spot Detection Systems (BSDS), in which a specified zone, or set of zones in the proximity of the vehicle, is monitored for the presence of other road users or hazardous objects, have been developed. A typical BSDS may monitor at least one zone approximately one traffic lane wide on the left- or right-hand side of the vehicle, and generally from the driver's position to approximately 10 m rearward. The objective of these systems is to provide the driver an indication of the presence of other road users located in the targeted blind spot.
Imaging systems have been developed in the prior art, such as discussed above, to perform this function, providing a visual, audio or tactile warning to the driver should a lane change or merge maneuver be attempted when another road user or hazard is detected within the monitored zone or zones. These systems are typically used in combination with a system of rearview mirrors in order to determine if a traffic condition suitable for a safe lane change maneuver exists. They are particularly effective when the detected object is moving at a low relative velocity with reference to the detecting vehicle, since the detected object may spend long periods of time in the blind spot and the driver may lose track of surrounding objects. However, prior art systems are inadequate in many driving conditions.
Known lane departure warning systems typically rely on visually detecting markers on the road on both sides of the vehicle for lane center determination. These markers must be fairly continuous or frequently occurring and generally must exist on both sides of the vehicle for the lane center position to be determined. Failure to detect a marker usually means failure of the departure-warning algorithm to adequately recognize a lane change event.